Instituto de Óptica “Daza de Valdés”

The Institute of Optics has participated in the BxDiff project within the EMPIR program that has developed a traceable measurement system of the total appearance of surfaces with complex visual effects.


Madrid / February 27, 2023

Today, research is being done in the field of metrology to develop a system for measuring the appearance of a surface, which gives us values that completely define the joint contribution of color, gloss, texture and translucency.

Within these efforts, the BxDiff project, funded by the European Association of National Metrology Institutes (EURAMET) in the EMPIR program, has achieved interesting results, which is why it has been selected by EURAMET among the success stories of its projects. A summary of it can be found summary in the news area of the EURAMET website.

Within this project, the Institute of Optics has actively participated, being responsible for the development of the translucency scale in a way traceable to the international system of units.

The “overall appearance” of an object is defined as the combined contribution of color, gloss, texture, and translucency. The appearance of an object depends on its shape and size, but also on factors such as viewing distance and lighting environment.

Silver scientific equipment composed of two legs that support a long shaft that has a tube that goes down to the center and various equipment of different shapes
Photograph of the goniospectrophotometer of the “Daza de Valdés” Institute of Optics, developed to carry out measurements of BRDF, BTDF and BSSRDF, and thus support the evaluation and definition of appearance measurement scales, such as color, brightness, translucency or texture. / Institute of Optics
New materials designed to produce complex visual effects such as iridescence, gloss or retroreflection are more difficult to characterize and require the development of new measurement methods, as well as the re-definition of relevant properties.

The BxDiff project

The EMPIR project ‘New quantities for appearance measurement’ (18SIB03, BxDiff) has defined and developed traceable references and measurement facilities for two spectrophotometric quantities necessary for the characterization of transparency and translucency, such as the distribution function of bidirectional transmittance (BTDF) and the bidirectional subsurface reflectance distribution function (BSSRDF). It has also managed to improve the measurement uncertainty and traceability at different scales of the bidirectional reflectance distribution function (BRDF), a property used to measure effects such as iridescence and brightness.

Crumpled metallic paper whose folds reflect light of different colors
Metallic and iridescent surface / Photo by Vinicius “amnx” Amano on Unsplash
As a consequence of this work, the measurement of the BSSRDF distribution function has been traceable to the International System of Measurements.
“Making the BSSRDF measurement in a way traceable to the SI has a direct impact on industries such as cosmetics, automotive, plastic and paper, as well as image rendering software applications.” explains Joaquín Campos, head of the Optical Radiation Measurements group (GIMRO) of the IO-CSIC.

This EMPIR project is co-financed by the Horizon 2020 research and innovation program of the European Union and the States participating in EMPIR.

IO-CSIC Communication

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